The invention relates to a system for lifting and supporting an object; particularly to a two part jacking system including a power unit that can be used to place and elevate a jack stand for lifting and supporting a corner of a vehicle. The two part system is inherently safer to use than a conventional floor jack to elevate a vehicle, and which then requires the user to crawl under the vehicle to place a conventional jack stand adjacent to the elevated floor jack to support the load. The inventor of the present invention is a pioneer of the two part jacking system and holds numerous patents related to this technology.
Briefly, the two part jacking system consists of a mobile hydraulic power unit having a flat front base and extendable lift arms; and a separate mechanical jack stand that can be secured within the front base of the power unit, and elevated by extending the lift arms of the power unit, and locked by an integral ratchet locking mechanism. An example of the two part jacking system describing the power unit is shown in U.S. Pat. No. 7,410,148 (see FIGS. 1 and 9); and an example of the jack stand is also shown and described (see FIGS. 2-8).
In use, the jack stand is engaged within (and can be disengaged from) the front base of the power unit, and is maneuvered into position under a vehicle, to place the stand in a desired location for lifting and supporting a corner of the vehicle. The power unit is then activated by pumping the handle, raising the lift arms, and the stand is thereby extended vertically to the desired height, automatically locked in position, thus lifting and supporting the vehicle on the stand. By operating the controls at the end of the handle, the power unit lift arms are lowered, and the power unit is disengaged from the stand and pulled away, leaving the stand in position supporting the vehicle. The power unit is then free to position and extend another stand for elevating another corner of the same or another vehicle.
To lower the vehicle and remove the stand, the power unit is maneuvered into position to re-engage with the stand. By operating the controls at the end of the handle, the power unit is re-engaged with the base of the stand, and the lift arms are elevated to the height of the extended jack stand. The controls can then be operated to disengage the ratchet locking mechanism of the stand, and the lift arms are released to lower the stand to its original position. The power unit remains engaged with the stand and can be pulled away from the vehicle with the stand carried within the base.
The early designs of the power unit were adapted to carry several stands within the base; current models carry only one stand. Additional stands could be acquired to reload the power unit, so that a single power unit could be utilized to efficiently place and actuate numerous stands. Many commercial users employed the system for multiple ongoing projects, and would utilize all of their available stands. The power unit was thereafter useless until another stand was available, from a completed project, to be extracted and reused on a new project
The present inventor developed a “bridge” lifting plate positioned to bridge between the forward ends of the lift arms and adapts the power unit to function as a hydraulic floor jack, to more fully utilize the power unit. The present inventor also developed a bridge plate that could travel along the lift arms, and that was biased by springs toward the forward ends of the lift arms and onto the leveling pads to provide an “automatic slide forward bridge”. The vertical housing of the jack stand would force the bridge rearward on the lift arms. When there were no more stands within the base of the power unit, (and when the lift arms were in the lowered position) the bridge would automatically slide forward onto the leveling pads at the forward ends of the lift arms. The power unit then functioned directly as a hydraulic floor jack.
The use of a slide forward bridge with the power unit acting as a floor jack must be utilized with a safety mechanism to lock the elevated lift arms in position, in the event of any decay of hydraulic pressure while elevated.
Such a safety mechanism was initially developed and described in U.S. Pat. No. 6,663,081. The mechanism included a pair of rack bars fixed to the bottom of the power unit and a pair of dogs translated with a push bar to engage the rack bars in the event of a hydraulic pressure failure. To lower the lift arms, the dogs were releasable with a set of cables and springs by a release lever prior to releasing the control valve of the hydraulic cylinder. This mechanism was functional, but did not provide the desired durability, and further required the operator to actuate the lever to release the dogs, and then the control knob to release the lift arms.
An improved safety mechanism was developed and described in U.S. Pat. No. 7,413,169 (see FIGS. 35-37). This mechanism involved a pair of rack bars fixed within a pair of U-channels that retained the ends of a push bar. The ends of the push bar each included an extendable dog to automatically engage the rack bars to lock the lift arms. The dogs were releasable, through cables and springs, by a release lever prior to release of the control valve of the cylinder. This design was functional, but still required the manual use of a control lever prior to release of the control valve. The cables and springs were not as durable as desired for the power unit.
It is an object of the present invention to provide a power unit having a safety mechanism that is reliable and durable for automatically locking the lift arms when they are raised, and which is automatically released with the control knob when the lift arms are lowered.